SODIUM. 267 



These salts may be obtained by processes analogous to those given 

 for the corresponding potassium compounds. 



Sodium compounds are nearly all white and are not volatile at or 

 below a red heat. 



Tests for sodium. 



(Sodium chloride, NaCl, may be used.) 



1. As all salts of sodium are soluble in water, we cannot precipi- 

 tate this metal in the form of a compound by any of the common 

 reagents. (Potassium antimoniate precipitates neutral solution of 

 sodium salts, but this test is not reliable.) 



2. The chief reaction for sodium is the flame-test, compounds of 

 sodium imparting to a colorless flame a yellow color, which is very 

 intense. A crystal of potassium dichromate appears colorless, and a 

 paper coated with red mercuric iodide appears white when illuminated 

 by the yellow sodium flame. (The spectroscope shows a characteristic 

 yellow line.) 



As practically all substances contain a trace of some sodium com- 

 pound, and give a momentary sodium flame, the yellow flame can only 

 be used to judge the presence of an actual sodium compound when 

 it persists for a long time. 



Lithium, Li = 6.98. Found in nature in combination with silicic acid in 

 a few rare minerals or as a chloride in some spring waters. Of inorganic 

 salts, lithium bromide and carbonate are official. Hydroxide, carbonate, and 

 phosphate of lithium are much less soluble than the corresponding com- 

 pounds of potassium and sodium. Sodium phosphate added to a strong solu- 

 tion of a lithium salt produces, on boiling, a white precipitate of lithium 

 phosphate, Li 3 PO 4 . Lithium compounds color the flame a beautiful crimson 

 or carmine-red. 



LiOH is soluble in 14.5 parts of water at 20 C., Li 2 CO 3 in 75 parts at 20 C., 

 and 140 parts of boiling water, Li 3 PO 4 in 2540 parts of plain water and 3920 

 parts of ammoniacal water. 



Caesium, Cs, and Rubidium, Rb, occur widely distributed, but only in 

 small quantities, and generally in company with potassium, which they resem- 



QUESTIONS. What is the composition of common salt ; how is it found in 

 nature, and what is it used for? Describe Leblanc's and the Solvay process 

 for manufacturing sodium carbonate on a large scale. How much water is in 

 100 pounds of the crystallized sodium carbonate ? What is Glauber salt, and 

 how is it made ? State the composition of disodium hydrogen phosphate, and 

 how is it prepared from calcium phosphate? What difference exists between 

 sodium carbonate and bicarbonate both in regard to physical and chemical 

 properties? Give the composition of sodium thiosulphate; what is it used for? 

 Which sodium salts are. soluble, and which are insoluble? How does sodium 

 and how does lithium color the flame? Which lithium salts are official? 



